FIG. 3(a) is a cross-sectional view illustrating an effective refractive index waveguide type semiconductor laser device using materials containing AlGaAs described in, for example, an article by Y. Mihashi, Y. Nagai, H. Matsubara and K. Ikeda, entitled "A Novel Self-Aligned Laser with Small Astigmatism Grown by MO-CVD", Extended Abstracts of 17th Conference on Solid State Devices and Materials, 1985, pp. 63-66. In FIG. 3(a), reference numeral 1 designates a substrate comprising p type GaAs. A p type Al.sub.0.43 Ga.sub.0.57 As layer 2 having a thickness of 1 micron is disposed on the substrate 1. An n type GaAs current blocking layer 3 having a thickness of 1 micron is disposed on the p type AlGaAs layer 2. A p type Al.sub.0.43 Ga.sub.0.57 As cladding layer 4 having a thickness of 1 micron is disposed on the current blocking layer 3. An undoped Al.sub.0.07 Ga.sub.0.93 As active layer 5 having a thickness of 0.07 micron is disposed on the cladding layer 4. An n type Al.sub.0.43 Ga.sub.0.57 As cladding layer 6 having a thickness of 1.3 micron is disposed on the active layer 5. An n type GaAs contact layer 7 having a thickness of 1 micron is disposed on the cladding layer 6. In addition, reference numeral 8 designates a stripe-shaped groove provided on the current blocking layer 3, and reference numeral 9 designates an oscillating region.
A semiconductor laser device having the structure as shown in FIG. 3(a) is generally referred to as an SBA (Self-aligned structure laser with bent active layer) laser.
Description is now made of a method of fabricating this laser. First, a p type AlGaAs layer 2 and an n type GaAs current blocking layer 3 are epitaxially grown on a (100) p type GaAs substrate 1 and then, a stripe-shaped groove 8 serving as a current path is formed on the current blocking layer 3 along the [011] direction. Then, a p type AlGaAs cladding layer 4, an undoped AlGaAs active layer 5, an n type AlGaAs cladding layer 6, and an n type GaAs contact layer 7 are sequentially grown by MOCVD (Metal Organic Chemical Vapor Deposition). When materials containing AlGaAs are grown by MOCVD, the growth proceeds in such a manner as to maintain the shape of the stripe-shaped groove 8. Consequently, the laser structure as shown in FIG. 3(a) is achieved. This characteristics is inherent to MOCVD. In such a structure with a grown layer that is bent, current is efficiently concentrated in an oscillating region 9. Accordingly, the threshold current of laser oscillation can be reduced. In addition, the SBA laser is constructed such that the cladding layer 4 comprising p type Al.sub.0.43 Ga.sub.0.57 exists on right and left sides of the active layer 5 comprising Al.sub.0.07 Ga.sub.0.93 As at the oscillating region 9. Accordingly, an effective refractive index difference occurs in a lateral direction of the oscillating region 9. Consequently, the SBA laser has the advantages that a lateral mode can be stably controlled and astigmatism can be reduced.
Although the SBA laser has the above-described advantages, the same structure is achieved by materials containing AlGaInP as shown in FIG. 3(b). In FIG. 3(b), reference numeral 10 designates a p type AlGaInP cladding layer having a thickness of 0.8 to 1 micron, reference numeral 11 designates a GaInP active layer having a thickness of 0.07 micron, and reference numeral 12 designates an n type AlGaInP cladding layer having a thickness of 0.8 to 1 micron. Thus, when a stripe-shaped groove is buried by growing materials containing AlGaInP, abnormal growth occurs. Consequently, a good SBA laser structure such as that using materials containing AlGaAs can not be achieved using materials containing AlGaInP.
The conventional semiconductor laser device is constructed as described above. Accordingly, the semiconductor laser device has the disadvantage in that it is difficult to achieve the above-described good SBA structure using the materials containing AlGaInP.